The present invention relates to combination vaccines or multivalent vaccines comprising Lawsonia intracellularis (L. intracellularis) antigen and at least one further antigen of one or more swine pathogens other than L. intracellularis. More particularly, the present invention provides immunogenic compositions effective at inducing an immune response against infection by L. intracellularis and at least one other disease-causing organism for swine.
L. intracellularis, the causative agent of porcine proliferative enteropathy (“PPE”), affects virtually all animals, including: rabbits, ferrets, hamsters, fox, horses, and other animals as diverse as ostriches and emus. PPE is a common diarrheal disease of growing-finishing and young breeding pigs characterized by hyperplasia and inflammation of the ileum and colon. It often is mild and self-limiting but sometimes causes persistent diarrhea, severe necrotic enteritis, or hemorrhagic enteritis with high mortality.
The bacteria associated with PPE have been referred to as “Campylobacter-like organisms.” S. McOrist et al., Vet. Pathol., Vol. 26, 260-264 (1989). Subsequently, the causative bacteria have been identified as a novel taxonomic genus and species, vernacularly referred to as Ileal symbiont (IS) intracellularis. C. Gebhart et al., Int'l. J. of Systemic Bacteriology, Vol. 43, No. 3, 533-538 (1993). More recently, these novel bacteria have been given the taxonomic name Lawsonia (L.) intracellularis. S. McOrist et al., Int'l. J. of Systemic Bacteriology, Vol. 45, No. 4, 820-825 (1995). These three names have been used interchangeably to refer to the same organism as further identified and described herein. Koch's postulates have been fulfilled by inoculation of pure cultures of L intracellularis into conventionally reared pigs; typical lesions of the disease were produced, and L intracellularis was reisolated from the lesions. The more common, nonhemorrhagic form of the disease often affects 18- to 36-kg pigs and is characterized by sudden onset of diarrhea. The feces are watery to pasty, brownish, or faintly blood stained. After ˜2 days, pigs may pass yellow fibrinonecrotic casts that have formed in the ileum. Most affected pigs recover spontaneously, but a significant number develop chronic necrotic enteritis with progressive emaciation. The hemorrhagic form is characterized by cutaneous pallor, weakness, and passage of hemorrhagic or black, tarry feces. Pregnant gilts may abort. Lesions may occur anywhere in the lower half of the small intestine, cecum, or colon but are most frequent and obvious in the ileum. The wall of the intestine is thickened, and the mesentery may be edematous. The mesenteric lymph nodes are enlarged. The intestinal mucosa appears thickened and rugose, may be covered with a brownish or yellow fibrinonecrotic membrane, and sometimes has petechial hemorrhages. Yellow necrotic casts may be found in the ileum or passing through the colon. Diffuse, complete mucosal necrosis in chronic cases causes the intestine to be rigid, resembling a garden hose. Proliferative mucosal lesions often are in the colon but are detected only by careful inspection at necropsy. In the profusely hemorrhagic form, there are red or black, tarry feces in the colon and clotted blood in the ileum. Altogether, L. intracellularis is a particularly great cause of losses in swine herds in Europe as well as in the United States.
L. intracellularis is an obligate, intracellular bacterium which cannot be cultured by normal bacteriological methods on conventional cell-free media and has been thought to require cells for growth. S. McOrist et al., Infection and Immunity, Vol. 61, No. 19, 4286-4292 (1993) and G. Lawson et al., J. of Clinical Microbiology, Vol. 31, No. 5, 1136-1142 (1993) discuss cultivation of L. intracellularis using IEC-18 rat intestinal epithelial cell monolayers in conventional tissue culture flasks. In U.S. Pat. Nos. 5,714,375 and 5,885,823, both of which patents are herein incorporated by reference in their entireties, cultivation of L. intracellularis in suspended host cells was described.
Pathogenic and non-pathogenic attenuated bacteria strains of L. intracellularis are well known in state of the art. For example, WO 96/39629 and WO 05/011731 describe non-pathogenic attenuated strains of L. intracellularis. Further attenuated bacteria strains of L. intracellularis are known from WO 02/26250 and WO 03/00665.
Actinobacillus pleuropneumonia, also known as APP and Haemophilus pleuropneumonia, is caused by the Actinobacillus pleuopneumonia bacteria. There are currently 15 serovars described and the severity of the clinical signs differ between the different serovirus and the presence of other factors. Serovirus 1, 5, 9, 10, and 11 are considered to be more virulent. Additionally, serovirus 1, 9, and 11; 2, 6, and 8; and 4 and 7 may cross-react. Pigs of all ages are susceptible. Clinical signs are a sudden illness that results in animals lying down a lot and presenting a high rectal temperature of 41.5° Celsius. Animals are generally anorexic and do not drink, their extremities become cyanotic and cold to the touch. Cyanosis can spread to the whole body and severe breathing difficulties, often with mouth breathing, develop before death. Blood-stained froth can be seen at the mouth and nostrils and death generally occurs within 24-48 hours. Acute clinical signs include a high percentage of animals in a group being depressed and lying down, high rectal temperatures of 40.5-41° Celsius, anorexia, lack of drinking, severe respiratory distress, coughing, mouth breathing, cyanosis, vomiting, and abortion. Sub-acute clinical signs include intermittent coughing in a group of pigs, a general loss of appetite, and a reduction in growth. Cyrovar type 3 presents with arthritis, endocarditis, and abscesses. In chronically effected herds, daily weight gain may not be affected, but an intermittent cough may be heard.
Bordetella bronchiseptica Infection: Asymptomatic pigs may harbor this gram-negative, nonsporeforming rod in the nasal cavity and trachea. Subclinical infections are more common in colonies, but epizootic outbreaks can occur rapidly with high morbidity and mortality. Transmission is by aerosol or, in its genital form, through sexual contact. Genital infection may cause infertility, stillbirths, and abortions. Several other species may be asymptomatic upper respiratory carriers, including dogs, cats, rabbits, rats, and mice. Contact with these potential hosts should be avoided. Necropsy may reveal lung consolidation and mucopurulent exudate in the bronchi, trachea, and middle ear.
Spirochaetal colitis is caused by the Brachyspira pilosicoli bacteria. This infection generally affects 10-20 week old growers/finishers. It is characterized by a non-fatal wasting diarrhea of growing pigs that results in an increased number of days needed to finish. The diarrhea also results in reduction in feed efficiency and produces watery diarrhea or loose stools. About half of the pigs may show transient to persistent, to watery to mucoid green to brownish diarrhea, without blood. The clinical signs are more common 10-14 days after mixing and changing of the feed. Swine dysentery is caused by the bacteria Brachyspira hyodysentheriae. There are twelve known sero-types at this time. Clinical signs in established herd include diarrhea, a rapid loss of condition in some pigs, a hairy appearance, dehydration, painful abdomen, and the death of one or two pigs before other pigs show any signs. In a key outbreak in naïve herds, all age groups from suckling piglets to adult sows can be effected.
Brucellosis is caused by bacteria of the genus Brucella and is characterized by abortion, retained placenta, infertility, orchitis in boars and severe metritis in sows. In piglets, the disease is characterized by posterior paralysis and lameness. The disease in pigs is caused almost exclusively by Brucella suis biovars 1, 2, and 3. A number of other mammals can carry and transmit Brucella suis to pigs. Infection spreads rapidly and causes many abortions in unvaccinated herds. Transmission occurs mainly by contact with another pig, although venereal transmission is possible. Serological diagnosis can be difficult due to a relatively common organism, Yersinia enterocolitica O:9 which shares a common antigen with Brucella and often causes false positive results. Post-mortem lesions usually include metritis and orchitis, and can include abscessation, sometimes with necorsis foci in the liver.
Porcine Epidemic Diarrhea (PED) is caused by a coronavirus somewhat similar to that which causes TGE. This virus is widespread in Europe. The virus damages the villi in the gut thus reducing the absorptive surface, with attendant loss of fluid and dehydration. After introduction of the virus into a susceptible breeding herd, a strong immunity develops over two to three weeks. The colostral immunity then protects the piglets. The virus usually disappears spontaneously from breeding herds particularly small ones (<300 sows). Acute outbreaks of diarrhea occur when the virus is first introduced into a susceptible population. In such cases up to 100% of sows may be affected, showing a mild to very watery diarrhea. Two clinical pictures are recognized: PED Type I only affects growing pigs whereas PED Type II affects all ages including sucking pigs and mature sows. The incubation period is approximately 2 days and diarrhea lasts for 7 to 14 days. In sucking pigs the disease can be mild or severe with mortalities up to 40%. In large breeding herds, particularly if kept extensively, not all the females may become infected the first time around and there may be recrudescence. This only occurs in piglets suckling from sows with no maternal antibodies and is therefore sporadic.
Clostridium is a ubiquitous gram-positive bacteria, of the family clostridiaceae, usually found in the soil, but which also occurs naturally in the gut of most animals. C. difficile infections in swine are characterized by severe mesocolonic edema, diarrhea, and edema in other tissues such as the hydrothorax. Clostridium enteritis in swine is caused by C. perfringens, and is characterized by chronic enteritis, which is accompanied by diarrhea, weight loss and fever. Infection with C perfringens types A, B and C causes severe enteritis, dysentery, toxemia, and high mortality in young calves. Types B and C both produce the highly necrotizing and lethal β toxin that is responsible for the severe intestinal damage. This toxin is sensitive to proteolytic enzymes, and disease is associated with inhibition of proteolysis in the intestine. Sow colostrum, which contains a trypsin inhibitor, has been suggested as a factor in the susceptibility of young piglets. The disease can cause sudden death in piglets less than one week old, and is most common within 3 days of birth. In older piglets, Clostridium enteritis causes a thickening of the small intestine making absorption of food and nutrients difficult. Piglets usually die as a result of a combination of the infection and lack of nutrients. Death may occur in a few hours, but less severe cases survive for a few days, and recovery over a period of several days is possible. Hemorrhagic enteritis with ulceration of the mucosa is the major lesion in all species. Grossly, the affected portion of the intestine is deep blue-purple and appears at first glance to be an infarction associated with mesenteric torsion. Smears of intestinal contents can be examined for large numbers of gram-positive, rod-shaped bacteria, and filtrates made for detection of toxin and subsequent identification by neutralization with specific antiserum. Clostridium novyi has been suspected but not yet confirmed as a cause of sudden death in cattle and pigs fed high-level grain diets, and in which pre-existing lesions of the liver were not detectable. The lethal and necrotizing toxins (primarily a toxin) damage hepatic parenchyma, thereby permitting the bacteria to multiply and produce a lethal amount of toxin. Usually, death is sudden with no well-defined signs. Affected animals tend to lag behind the herd, assume sternal recumbency, and die within a few hours. Most cases occur in the summer and early fall when liver fluke infection is at its height. The disease is most prevalent in 1- to 4-yr-old sheep and is limited to animals infected with liver flukes. Differentiation from acute fascioliasis may be difficult, but peracute deaths of animals that show typical lesions on necropsy should arouse suspicion of infectious necrotic hepatitis. The most characteristic lesions are the grayish yellow necrotic foci in the liver that often follow the migratory tracks of the young flukes. Other common findings are an enlarged pericardial sac filled with straw-colored fluid, and excess fluid in the peritoneal and thoracic cavities. Usually, there is extensive rupture of the capillaries in the subcutaneous tissue, which causes the adjacent skin to turn black (hence the common name, black disease). Clostridium septicum is found in soil and intestinal contents of animals (including man) throughout the world. Infection ordinarily occurs through contamination of wounds containing devitalized tissue, soil, or some other tissue-debilitant. Wounds caused by accident, castration, docking, insanitary vaccination, and parturition may become infected. General signs, such as anorexia, intoxication, and high fever, as well as local lesions, develop within a few hours to a few days after predisposing injury. The local lesions are soft swellings that pit on pressure and extend rapidly because of the formation of large quantities of exudate that infiltrates the subcutaneous and intramuscular connective tissue of the affected areas. Accumulations of gas are uncommon. Malignant edema associated with lacerations is characterized by marked edema, severe toxemia, and death in 24-48 hr. Tetanus toxemia is caused by a specific neurotoxin produced by Clostridium tetani in necrotic tissue. Almost all mammals, including swine, are susceptible to this disease. Although tetanus is worldwide in distribution, there are some areas, such as the northern Rocky Mountain section of the USA, where the organism is rarely found in the soil and where tetanus is almost unknown. In general, the occurrence of C tetani in the soil and the incidence of tetanus in man is higher in the warmer parts of the various continents. Clostridium tetani, an anaerobe with terminal, spherical spores, is found in soil and intestinal tracts. In most cases, it is introduced into the tissues through wounds, particularly deep puncture wounds that provide a suitable anaerobic environment.
Escherichia coli is a bacteria of the enterbacteriaceae family and is one of the main types of bacteria naturally occurring in the small intestines of all mammals. Although usually harmless, some E coli strains can produce a number of exo- and endotoxins that cause infection and disease. Heat-labile (LT) and heat-stable (ST) exotoxins are actively produced by some strains and are responsible for causing scour. Shigela-like toxin type II variant (SLT-IIe), Stx2e and verotoxin edema disease act on the wall of the small arteries resulting in oedema. Endotoxins, such as Lipid A, play a role in mastitis and urinary tract infections. E. coli infection is characterized by a number of different symptoms depending on the particular strain involved, including diarrhea, sunken eyes, unthriftiness, visible weight loss, stunted growth, depression, bowel edema, mastitis, cystitis, pyelonephritis and death. E. coli can be classified and coded by their cell wall (O antigens) and fimbriae (F antigens). For example, scour is often associated with E. coli Abbotstown: O147, F4, F5, whereas bowel edema is associated with F18 fimbriae. Correctly identifying the code is essential to the selection of the correct vaccine. E. coli infections compromise a pig's immune system and deaths are often the result of secondary infections and disease.
Encephalomyocarditis, or EMC, infects and causes disease in a wide range of vertebrate animals but pigs appear to be the most susceptible of farm animal species. The virus, Encephalomyocarditis virus is world-wide but differs in pathogenicity and virulence in different countries and regions. In most countries of Europe, particularly those in the EU, it tends to be relatively mild or non-pathogenic and disease in pigs is rarely diagnosed. In Australia the strains appear to be much more virulent for pigs than those in New Zealand. Virulent strains in Florida, the Caribbean and probably Central America damage the heart and cause death whereas those in the Mid-West of the US tend to cause reproductive problems. Clinical disease in pigs tends to occur when rat numbers increase to plague levels. Pigs can be infected from rats or from rat-contaminated feed or water. It does not seem to spread very readily between pigs. In affected herds there are usually no clinical signs in weaned and growing pigs.
Eperythrozoonosis is a Rickettsial (haemotrophic) disease caused by Eperythrozoon suis, an extracellular bacterial organism that adheres to pig erythrocyte membranes, inducing its deformation and damage. The disease is characterized by anemia and icterus (yellow discoloration of mucous membranes, sclera and inner ears). It can lead to poor conception rates, other vague reproduction problems and even death.
Swine erysipelas is caused by a bacterium, Erysipelothrix rhusiopathiae that is found in most if not all pig farms. Up to 50% of animals may carry it in their tonsils. It is always present in either the pig or in the environment because it is excreted via saliva, feces or urine. It is also found in many other species, including birds and sheep and can survive outside the pig for a few weeks and longer in light soils. Thus it is impossible to eliminate it from a herd. Infected feces are probably the main source of infection, particularly in growing and finishing pens. The bacterium alone can cause the disease but concurrent virus infections, such as PRRS or influenza, may trigger off outbreaks. Disease is relatively uncommon in pigs under 8-12 weeks of age due to protection provided by maternal antibodies from the sow via the colostrum. The most susceptible animals are growing pigs, non-vaccinated gilts and up to 4th parity sows. The organism multiplies in the body, and invades the bloodstream to produce a septicemia. The rapidity of multiplication and the level of immunity in the pig then determines the clinical symptoms.
Glässers Disease is caused by the bacterium Haemophilus parasuis (Hps), of which there are at least fifteen different types. It is found throughout the world and organisms are present even in high health herds. If such herds are set up using SPF or MEW techniques and are free from Hps it can be devastating when they first become contaminated, producing an anthrax-like disease with high mortality in sows. In the majority of herds in which the bacterium is endemic, sows produce a strong maternal immunity which normally persists in their offspring until 8 to 12 weeks of age. As a result, the effects of the infection in weaners are usually nil or minimal. Disease may however be seen in suckling pigs. Pigs usually become sub-clinically infected when still protected by maternal antibody and then stimulate their own immune response. If however, the maternal immunity wears off before they become infected they may develop severe disease. This is usually sometime after weaning. It can also act as a secondary pathogen to other major diseases particularly enzootic pneumonia (EP) (Mycoplasma hyopneumoniae). Outbreaks of disease are sometimes experienced in sucking pigs, particularly in gilt herds. Hps attacks the smooth surfaces of the joints, coverings of the intestine, lungs, heart and brain, causing pneumonia, heart sac infection, peritonitis and pleurisy. It is respiratory spread. Disease caused by Hps is rare in sows unless the dry sow is naïve. Lameness or stiffness, slight swellings over the joints and tendons, and rarely meningitis, are occasionally seen in gilts. In piglets, acute disease presents with rapidly depressed pigs with elevated temperature, inappetence, and a reluctance to rise. One characteristic feature is a short cough of 2-3 episodes. Sudden death in good sucking piglets is not uncommon. Hps is also known to cause individual cases of arthritis and lameness with fever and inappetence. Chronic disease is characterized by pale and poor growing pigs. Sudden death may also occur. For weaners and growers, pigs with Glässers Disease become rapidly depressed or may be just found dead. Other symptoms include elevated temperature, anorexia, a reluctance to rise, nervous signs such as fits and convulsions including meningitis, and poor pigs, that are wasting and hairy often result. In young growing pigs, the following symptoms are most common: fever, mild meningitis, arthritis, lameness, pneumonia, heart sac infection, peritonitis and pleurisy. Again, a characteristic feature is a short cough of only 2-3 episodes.
Leptospirosis is a contagious disease of animals, including man, caused by various immunologically distinct leptospiral serovars, most of which are regarded as subgroups of Leptospira interrogans. There are five serovars and groups which are important in swine: pomona, australis, tarassovi, canicola, icterohaemorrhagicae, and grippotyphosa. Infections may be asymptomatic or cause various signs, including anorexia, pyrexia, listlessness, jaundice, abortions, still births and other vague reproductive problems, and death. After acute infection, leptospires frequently localize in the kidneys or reproductive organs consisting of scattered small grey foci of a focal interstitial nephritis, and are shed in the urine, sometimes in large numbers for months or years. Because the organisms survive in surface waters for extended periods, the disease is often waterborne. In the USA, the disease is primarily due to the serovars Leptospira hardjo, Leptospira pomona, and Leptospira grippotyphosa. Diagnosis can be difficult because antibody titers can be transient, lasting less than a month. Further, Leptospira can also be found in healthy animals. L. australis serovar bratislava is most commonly associated with reproductive problems. Chronically infected herds display abortions, still births and weak piglets.
Tuberculosis affects mammals, including people, birds, and swine. The causal organism, Mycobacterium tuberculosis, is sub-classified into types, human, bovine and avian. The avian type is referred to as M. avium or more often the avian/intracellulare complex because it is not a uniform species. M. avium itself infects mainly birds but is also found in the environment along with M. intracellulare which is predominantly saprophytic or free living. Pigs are rarely infected by the human or bovine types but are commonly infected by the avian/intracellulare complex. The avian/intracellulare complex also causes sub-clinical non-progressive infection in healthy people. The main concern is that it could cause more serious disease in immuno-suppressed people and people with AIDS. In most countries if lesions are found in the neck at slaughter the whole head is condemned and if they are found in the mesenteric lymph nodes which drain the intestines the offals are condemned. If they are more widespread in the body, which is rare, the whole carcass may be condemned or cooked. If small lesions are missed by the meat inspector normal kitchen cooking destroys the organism. In all pigs, infection causes small nodules in the lymph nodes of the neck and those that drain the small intestine. In the great majority of cases the lesions are non-progressive, they do not spread through the body, do not make the pig ill and are not excreted. There are no clinical symptoms and there is no difference in performance between infected and non-infected pigs.
Mycoplasma hyopneumoniae (M hyo) is a small bacterium (400-1200 nm) classified in the mycoplasmataceae family. M hyo is associated with Enzootic Pneumonia, a swine respiratory disease commonly seen in growing and finishing pigs. M hyo attacks the cilia of epithelial cells of the windpipe and lungs, causing the cilia to stop beating (ciliostasis) and eventually causing areas of the lungs to collapse. Depending on the extent of the disease, daily live weight gain of infected swine can be reduced by up to 17%. Enzootic Pneumonia is widespread in swine populations and present in almost every swine herd. M hyo is considered to be a primary pathogen that facilitates entry of PRRSV and other respiratory pathogens into the lungs. Three separate strains, 232, J & 7448 have had their genomes sequenced (Minion et al., J. Bacteriol. 186: 7123-33, 2004; Vasconcelos et al., J. Bacteriol. 187: 5568-77, 2005).
Parvovirus is a disease characterized by reproductive problems in pigs. The causal agent is a small DNA non-enveloped virus. Fetuses are the only affected group and the effect on the fetus depends upon the age at which it becomes infected. At 10-30 days of age, infection results in death and reabsorption of the fetus. Between 30-70 days of age, infection results in death and mummification. And from 70 days to term, infection results in the birth of weak piglets and mummification. The disease is able to cross the placenta and then move to each fetus along the uterus. In the sow, the clinical signs are still births, mummified piglets, embryonic deaths, infertility, and the production of a significantly reduced number of live-born offspring. Abortion is not a characteristic feature of parvovirus infection.
Pneumonic pasteurellosis is caused by Pasteurella multocida. Infection by the causal agent generally represents the final stage of the post-weaning respiratory syndrome. Clinical signs appear in three forms, the acute form is most commonly associated with P. multocida serotype B. Animals present with dyspnea, labored breathing, thumping, high fever (42.2 Celsius), prostration, and finally death. In some cases the abdomen becomes purple with discoloration. A second form is a sub-acute form characterized by pleuritis, coughing, and difficulty in breathing. Pigs can lose significant amounts of weight and may have poor or no growth with serious consequences in pig flow. The chronic form presents with the occasional cough, thumping, and little or no fever. This form generally affects pigs from 10-16 weeks of age.
Porcine circovirus is a small (17-22 nm in diameter), icosahedral, non-enveloped DNA virus, which contains a single-stranded circular genome. Porcine circovirus type 2 PCV2 shares approximately 80% sequence identity with porcine circovirus type 1 (PCV1). However, in contrast with PCV1, which is generally non-virulent, swine infected with PCV2 exhibit a syndrome commonly referred to as Post-weaning Multisystemic Wasting Syndrome (PMWS). PMWS is clinically characterized by wasting, paleness of the skin, unthriftiness, respiratory distress, diarrhea, icterus, and jaundice. In some affected swine, a combination of all symptoms will be apparent while other swine will only have one or two of these symptoms. During necropsy, microscopic and macroscopic lesions also appear on multiple tissues and organs, with lymphoid organs being the most common site for lesions. A strong correlation has been observed between the amount of PCV2 nucleic acid or antigen and the severity of microscopic lymphoid lesions. Mortality rates for swine infected with PCV2 can approach 80%.
Porcine Reproductive and Respiratory Syndrome (PRRS) is caused by a virus which was first isolated and classified as an arterivirus as recently as 1991. The disease syndrome had been first recognized in the USA in the mid 1980's and was called “mystery swine disease”. It has also been called blue ear disease. The name porcine arterivirus has been proposed recently. The virus of PRRS has a particular affinity for the macrophages particularly those found in the lung. Macrophages are part of the body defenses. Those present in the lung are called alveolar macrophages. They ingest and remove invading bacteria and viruses, but not in the case of the PRRS virus. Instead, the virus multiplies inside them producing more virus and killing the macrophages. Once it has entered a herd it tends to remain present and active indefinitely. Up to 40% of the macrophages are destroyed which removes a major part of the body's defense mechanism and allows bacteria and other viruses to proliferate and do damage. A common example of this is the noticeable increase in severity of enzootic pneumonia in grower/finisher units when they become infected with PRRS virus. It may take up to a year for all breeding stock, particularly in large herds, to become infected for the first time and although the virus appears to spread rapidly in a herd it may be some 4-5 months before at least 90% of the sows have become sero-positive. Some sows remain naive. Furthermore, it is not uncommon for sow herds 1-2 years after infection to contain less than 20% of serological positive animals. This does not however necessarily mean they are not still immune nor does it mean that they have stopped passing on immunity to their offspring. Adult animals shed virus for much shorter periods of time (14 days) compared to growing pigs which can excrete for 1-2 months. The clinical picture can vary tremendously from one herd to another. As a guide, for every three herds that are exposed to PRRS for the first time, one will show no recognizable disease, the second would show mild disease and the third, moderate to severe disease. The reasons for this are not clearly understood. However the higher the health status of the herd, the less severe are the disease effects. It may be that the virus is mutating as it multiplies, throwing up some strains that are highly virulent and some that are not. PRRS infects all types of herds including ones with high or ordinary health status and both indoor and outdoor units, irrespective of size.
Pseudorabies, also known as porcine rabies virus, or Suid herpes virus in which the causal agent is an enveloped herpes DNA virus. In naïve herds, neonatal pigs present with a range of severe central nervous signs from fitting to severe in coordination. Posterior paralysis may result in piglets sitting in a manner that resembles dogs. Additionally, mortality is high. In weaned pigs, the central nervous signs may be reduced, but may be accompanied by an increase in respiratory signs. Oftentimes, respiratory diseases are associated with secondary infections. Weaned pigs can waste and suffer ill thrift and are often stunted. In growing pigs, the central nervous signs continue to reduce while the respiratory signs increase. The degree of respiratory disease depends on the presence and severity of secondary infections. In adults, reproductive signs predominate. Sows may abort and animals infected close to term are likely to give birth to stillborn or weak piglets. In established herds, there may be few clinical signs.
Rotavirus infection is a virus infection that is widespread in pig populations. It is present in most if not all pig herds with virtually a 100% sero-conversion in adult stock. A further epidemiological feature is its persistence outside the pig where it is resistant to environmental changes and many disinfectants. Maternal antibodies persist for 3-6 weeks after which pigs become susceptible to infection but exposure does not necessarily result in disease. It is estimated that only 10-15% of diarrheas in pigs are initiated by a primary rotavirus infection. In a mature herd disease appears after piglets are 7 to 10 days of age. It becomes progressively less important with age. However if pathogenic strains of E. coli are present, severe disease can occur with heavy mortality.
Infection with Salmonella spp can produce diarrhea in animals of all ages, especially those that are stressed, closely stocked, or exposed to a heavily contaminated feed or water supply. Salmonellosis is caused by many species of salmonellae and characterized clinically by one or more of three major syndromes-septicemia, acute enteritis, and chronic enteritis. The incidence has increased with the intensification of livestock production. Although various types of Salmonella can cause infections in pigs, the classic salmonellas found in swine are S. choleraesuis and S. typhimurium. Their resulting clinical patterns of most salmonella are not distinct and different species of salmonellae tend to differ in their epidemiology. Plasmid profile and drug-resistance patterns are sometimes useful markers for epidemiologic studies. Septicemic salmonellosis is often associated with S choleraesuis. Infected piglets demonstrate a reluctance to move, anorexia, a high fever of 40.5 C-41.6 C, and may have a shallow cough. Piglets may also be found dead with cyanotic extremities. S choleraesuis is one of the rare diseases that can cause both pneumonia and diarrhea and mortality of infected piglets is often high. Enterocolitis is generally associated with the more common S typhimurium. Infections are characterized by yellow or watery diarrhea that may contain blood or mucus as the infection progresses. Mortality is low and often associated with dehydration and potassium deficiency from the diarrhea. Feces of infected animals can contaminate feed and water, fresh and processed meats from abattoirs, plant and animal products used as fertilizers or feedstuffs, pasture and rangeland, and many inert materials. Although S choleraesuis is rarely found in feed. It can also be passed directly from contact with an infected animal. Salmonella can survive for months in wet, warm areas such as in feeder pig barns or in water dugouts. Rodents and wild birds also are sources of infection. The prevalence of infection varies among species and countries and is much higher than the incidence of clinical disease, which is commonly precipitated by stressful situations such as sudden deprivation of feed, transportation, drought, crowding, parturition, and the administration of some drugs.
Exudative epidermitis is caused by the bacterium Staphylococcus hyicus which lives normally on the skin without causing disease. It is not known why sometimes it flares up and causes a dermatitis which oozes greasy fluid. It produces toxins which are absorbed into the system and damage the liver and kidneys. In the sucking piglet disease, is usually confined to individual animals, but it can be a major problem in new gilt herds and weaned pigs. During the days immediately preceding farrowing, the bacterium multiples profusely in the sow's vagina so that piglets are infected during the birth process or soon after. Symptoms in sows include uncommon but localized lesions that may be seen particularly behind the face and eyes. Severely affected piglets will die. In piglets, symptoms include localized lesions on the flanks and behind ears. Lesions usually commence with small, dark, localized areas of infection around the face or on the legs. The skin along the flanks the belly and between the legs changes to a brown color gradually involving the whole of the body. The skin becomes wrinkled with flaking of large areas and it has a greasy feel. In severe cases the skin turns black due to necrosis and the piglets die. A more localized picture is seen if the sow has passed some immunity to the piglet, with small circumscribed lesions approximately 5-10 mm in diameter that do not spread. For weaners and growers, symptoms usually commence about 3 days after weaning with localized, brown areas of infection or dermatitis around the face or on the legs, where the skin has been damaged. It may ulcerate. The skin along the flanks the belly and between the legs changes to a brown color gradually involving the whole of the body. The skin becomes wrinkled with flaking of large areas and progresses to a dark greasy texture and in severe cases turns black. Such cases usually die due to the toxins produced by the staphylococci organisms. In nurseries, up to 15% of the population may be involved and dehydration is common.
Streptococcal meningitis causes inflammation of the meninges which are the membranes covering the brain. In the sucking piglet, it is usually caused by bacteria of Streptococcus spp, e.g. Streptococcus suis, Haemophilus parasuis, or sometimes bacteria such as E. coli and other streptococci. S. suis has many serotypes. In most countries, S. suis type 1 is the main one in sucking piglets, but this may not be true in other countries. For example, in Denmark it is type 7. S. suis also causes joint problems particularly types 1 and 14. S. suis is carried for long periods in the tonsils and may be transmitted to the sucking piglet from the sow or from other piglets. The sow also provides a variable level of immunity in the colostrum. Streptococcal meningitis in sucking piglets is sporadic in individual piglets. Streptococcal meningitis may be worse in sucking pigs when the organism has been introduced into the herd for the first time, or where it is secondary to infection with PRRS.
Aujeszky's disease, or AD, is an important disease of pigs caused by swine herpes virus. The virus can remain hidden in nerves of the pig in a carrier state for long periods of time and then be reactivated. Once introduced into a herd the virus usually remains there and it can continually affect reproductive performance at varying levels. The virus can survive for up to three weeks outside the pig. Acute outbreaks of disease occur when virulent strains of the virus first infect an unvaccinated susceptible herd. The virus crosses the uterus and placenta and infects the fetuses. The pig is the main host. However, dogs and cattle may also become infected, show nervous signs, and die.
Swine Influenza Virus causes swine flu and belongs to the influenza Type A virus group. In naïve herds, clinical signs may present in explosive outbreaks with all or many animals becoming ill at the same time. Animals may present with inactivity, depression, huddling/pilling and anorexia. The animals are often mouth-breathing and breathing is labored. Coughing may ensue upon movement. Other clinical signs include a nasal discharge and puffy eyes with rectal temperatures between 40.5-41.5° Celsius. The high temperatures in a breeding stock can result in abortions, infertility, production of small weak litters, and increased still births. In established herds, annual reinfection appears.
Swine Pox is a disease which causes skin lesions, paules, pustules and scabs. It is caused by Swine pox virus.
Swine Vesicular Disease (SVD) is a different virus from the virus that causes foot and mouth disease (FMD). However, it produces a disease in pigs that is clinically indistinguishable from FMD. This disease should always be considered if sudden widespread lameness appears with vesicles or blisters on the snout, tongue and tops of the claws.
Transmissible gastroenteritis (TGE) is a disease of the intestines caused by a coronavirus (Transmissible gastroenteritis virus). It is in the same family as Porcine respiratory coronavirus, epidemic diarrhea virus, and Hemagglutinating encephalomyelitis virus. Initial clinical signs are watery diarrhea, vomiting, and anorexia. Piglets less than 21 days of age generally die, weaners become unthrifty, while growers, finishers, and adults are generally mildly affected and will survive if provided with adequate water.